1. Field of the Invention
The present invention relates to methods for rolling metal plate and more particularly to rolling method including multiple rolling steps.
2. Prior Art
In general, in the rolling work of metal plates, slabs manufactured by continuous casting equipment or a slabbing mill are rolled to a predetermined value of thickness by a thick sheet metal mill (a roughing mill and a finishing mill), and thereafter, cut into the dimensions of product by a shearing device or a gas cutter, to thereby obtain a product.
Detailed description will hereunder be given of a conventional rolling method. As shown in FIG. 1, first a slab 1 drawn out of a reheating furnace has its uneven section made even and uniform to obtain the standard thickness according to the broadening calculation by a rolling process which is the so-called sizing pass, and is rolled in the longitudinal direction through one pass or two to three passes, thus obtaining a condition indicated by reference numeral 2. Next, the rolled metal 2 is rotated through 90.degree. in a horizontal plane to obtain a condition indicated by reference numeral 3, sent to a rolling process which is the so-called broad side pass, and rolled to a given value in the width-wise direction, thus obtaining a condition indicated by reference numeral 4. Then, the rolled metal 4 is rotated through 90.degree. again in a horizontal plane to be restored to the original condition, i.e., a condition 5 where the longitudinal direction of said rolled metal is in parallel to the direction of the pass, suitably decreased in thickness in the longitudinal direction thereof, and thereafter sent to the so-called shape control pass which is the final rolling process by a finishing mill to thus obtaining a finished rolled metal 6.
Heretofore, the shape of the rolled metal 6 rolled to a given value of thickness by the shape control pass has been the ones shown in FIG. 2 or 3. Namely, as shown in FIG. 2, for example, the rolled metal 6 is generally spool-shaped, and more specifically the centers of the edge portions 6A is less in width than the opposite end portions. Furthermore, crop portions 6B are formed so as to bulge outwardly in the longitudinal direction of the rolled metal 6. Or, as shown in FIG. 3, the rolled metal 6 is generally barrel-shaped, and more specifically, the centers of edge portions 6A are larger in width than the opposite end portions. Additionally, the centers of the crop portions 6B are sunken inwardly in the longitudinal direction of the rolled metal 6.
Accordingly, to commercialize the rolled metal, it has been necessary that the edge portions 6A and crop portions 6B be cut off of the rolled metal 6 to obtain the contours shown by two-dotted chain lines in FIGS. 2 and 3. Thus, there has been presented such a disadvantage that there are many cut-off portions, thus lowering the yield.
The present invention is intended to eliminate the above disadvantage of the prior art.